Electric rheostat or heater



(NOMode1.) V

H. W. LEONARD.

ELECTRIC RHEOSTAT 0R HEATER.

No. 558,559. Patented Apr. 21, 1896.

WITNESSES: A? w IVTOR BY ATTORNEYS.

NDREW B.GRAHAM. PHOTO-UTHQWASHI NGYON (1.1:v

UNITED STATES PATENT OFFICE.

HARRY ARD LEONARD, OF EAST ORANGE, NEIV JERSEY.

ELECTRIC RHEOSTAT OR HEATER.

SPECIFICATION forming part of Letters Patent No. 558,559, dated April 21, 1896.

Application filed December 18,1895. Serial No. 572,514. (No model.)

T 64% whom it may concern:

Be it known that I, I'IARRY IVARD LEONARD, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented a certain new and useful Improvement in Electric Rheostats or Ileaters, of which the following is a specification.

My invention relates to devices in which electric energy is converted into heat and in which the conductor wherein the heat is generated is attached to a supporting-body by an insulating medium-such, for example, as enamel.

It is very important that the conductor be placed in very close proximity to its support, and from which itis well insulated, and that the best possible means be provided for al lowing the flux of heat from the conductor to the support, which is preferably of a material having a high specific capacity for heat, such as iron. It is also important that the medium which insulates the conductor from the support shall have as high specific insulation as possible. Itshould also be non-absorbent of moisture, and it should not be injuriously affected bybeing raised to the high temperature at which it is often desired to operate the apparatus. Enamel has these desirable properties, and when a conductor of, say, one-sixteenth of an inch in diameter or smaller is embedded in a layer of enamel on a support, as is the common practice today, a very perfect result is obtained; but I have found that if a'conductor whose diameter is much larger than one-sixteenth of an inch be embedded in enamel similar to the c011- ductor of smaller cross-section, and very large currents are sent through it suddenly, so as to heat up the conductor quickly, the expansion of the conductor in the direction normal to the surface of the supportbecomes so great as to cause the enamel to split off from the support and from the conductor itself, which not only makes the conductor unstable as re-' gards its form and position, but also interferes with the flux of heat by conduction to the support, and the cracking of the enamel opens up passages for moisture, making the apparatus liable to become short-circuited.

I have found in the construction of rheostats and heaters that it is not practicable to certain size.

embed in the enamel a conductor beyond a For example, it is not practi cable to embed a conductor of one-eighth of an inch in diameter, and yet in certain apparatus-such, for example, as feeder-equalizersa conductor of very large current capacity and very low resistance is required, and a conductor of one-eighth of an inch in diameter would be none too large.

The object of my invention is to overcome the difficulties in rheostats or heaters above mentioned and to produce a better and cheaper form of apparatus for dissipating a large amount of energy from a small surface, and especially when the apparatus is of a type having a low resistance and requiring a large current in its practical operation-such, for example, as a rheostat for a large motor 0pe atin g on a low-potential circuit such as is in common use.

I accomplish the objects of my invention by employing enamel for insulating the conduct-or and attaching it to the support, the conductor being only slightly embedded in the enamel, the most of its surface being exposed to the air and therefore free to expand and contract without subjecting the enamel to strains tending to crack the enamel and cause it to separate from the support.

I have found that a conductor of large crossscction can be enameled to a support by my method and subjected to a sudden and extremely large current relative to its carrying capacity without in any way damaging the apparatus, and that the apparatus can be operated at a much higher rate of dissipation of watts per square inch than was possible by former methods and apparatus.

My invention is illustrated in the accompanying drawings, which show a conductor A, of large cross-section, enameled to a supporting-body B by a layer of enamel C. An intermediate layer of material D is illustrated. This layer is what is known as the ground coat.

In Figure l the conductor A is shown as circular in cross-section, while in Fig. 2 it is illustrated as oval-shaped in cross-section,

and in Fig. 3 as rectangular in cross-section.

In commercial apparatus it will be understood, of course, that the form of cross-section of the conductor and its arrangement upon.

the supporting-body may be varied greatly; but the accompanyingdrawings serve to fully illustrate my invention,so that any one skilled in the art will readily be able to apply my invention to apparatus of practical commercial form. For instance, the conductor may be formed with an irregular surface to increase its radiating-surface, or it may be bent or shaped into various forms, as is the practice at present.

In all of the forms shown it will be readily seen that the conductor is free to expand in a direction at right angles to the support without placing any injurious strain upon the enamel, and that the expansion of the conductor in a direction parallel to the surface imparts astrain of compression. Such astrain the enamel can stand to a great extent without injury, and since this strain is generally in all directions parallel to the surface the effect is neutralized, and hence there is no tendency to strip the enamel from the supporting-body.

In using the term enamel in the specification and claims I intend to include any insulating material which has a high specific insulation, and which insulation is practically unaffected by the Working temperature of the apparatus, and which becomes adhesive at a high temperature and which does not absorb moisture to an injurious extent, and which serves to hold the conductor in its position relative to the support.

Vhat I claim is- 1. The combination of a conductor, a supporting-body, and a layer of insulating ma terial between the same and in which the conductor is partially embedded and which attaches the conductor to the supporting-body, substantially as and for the purpose set forth.

2. The combination of a conductor, a supporting-body, and a layer of enamel between the same and in which the conductor is partially embedded and which attaches the conductor to the supporting-body, substantially as and for the purpose set forth.

3. In an electric rheostat or heater, the combination of a conductor of large current capacity, a supporting-body, and a layer of enamel between the same and in which the conductor is partially embedded and which attaches the conductor to the supportingbody, substantially as and for the purpose set forth.

4. In an electric rheostat or heater, the combination of a partly-exposed conductor, a supporting-body, and a layer of enamel between the same which attaches the conductor to the support, whereby the heat developed in said conductor is dissipated partly by radiation and partly by conduction to the supporting-body, substantially as and for the purpose set forth.

5. The combination with a supportingbody, of a layer of insulating material, and a conductor having a practically rectangular cross-section partially embedded in said layer of insulating material, and whose longer dimension is normal to the surface of the insulating material, substantially as set forth.

6. The combination with a supportingbody, of a layer of insulating material, and a conductor of large current capacityand large radiating-surface partially embedded in said layer of insulating material, whereby the heat developed in said conductor is dissipated partly by radiation and partly by conduction to the supporting-body, substantially as set forth.

This specification signed and witnessed this 16th day of December, 1805.

Il. WARD LEONARD. lVitnesses:

EUGENE CONRAN, W. BELZER. 

